The present invention relates to the field of system analysis and diagnostics, particularly in a downhole network along a drill string used in oil and gas exploration, or along the casings and other equipment used in oil and gas production.
Many downhole systems have been developed which transmit data from one point to another, and the properties of the network may influence the performance of the system. Therefore, it may be useful to have tools that can test the properties of a network. Several apparatuses and methods have been developed to analyze the properties of a network.
U.S. Pat. No. 3,978,282 discloses an apparatus and method for measuring the characteristics of a network in which a substantially non-interfering, low-intensity sweeping test signal is transmitted along a network to be tested. A reference signal is transmitted along with a test signal for synchronizing the operation of tracking means.
U.S. Pat. No. 5,307,284 discloses a vector network analyzer, which utilizes a single voltage controlled oscillator to produce a sweep frequency over time, which is supplied to a device under test. The return signal from the device under test is delayed and mixed with the original signal to produce an intermediate frequency signal that is digitized and the data manipulated by a computer to measure the reflection coefficient or transmission coefficient of the device under test.
U.S. Pat. No. 4,739,325 discloses an apparatus and method for down-hole EM telemetry while drilling which utilizes a down-hole microprocessor unit and a surface data processing unit (computer) each of which continuously monitors, probes and sweeps the frequency spectrum with EM signals to determine an optimum frequency for signal transmission between the respective units via either the drill string, the surrounding strata, or both
U.S. patent application Ser. No. 10/708,775 filed Mar. 24, 2004 in the name of Hall, et al. discloses a method and apparatus for testing electromagnetic connectivity in a drill string. The method comprises transmitting a test signal along a transmission path in a drill string; receiving a reflection of the test signal; and determining from the reflection whether there is an interruption in the electromagnetic connectivity in the transmission path. In general, the apparatus comprises a signal generator for generating a test signal into the drill string; a receiver for receiving the reflection of the test signal; and means for determining from the reflection whether there is an interruption in the electromagnetic connectivity in the transmission path.